iMessage and ipad issues

My iphone6 and my iPad Air both have iMessage set up the same way:
same 2 email addresses + my phone number, conversations started from my phone number on both devices.
iMessage enabled on my Macbook Air as well.

With other Apple users, no problem.
But whenever I message with a friend of mine who has a Samsung Note2, the conversation only happens on my phone, not on my iPad or macbook.
This wasn't always the case, in fact until november 12, there were no issues.